1. Field of the Invention
The present invention generally relates to semiconductor integrated circuit manufacturing and, more particularly to a method of forming a conformal, homogeneous dielectric film such as a silicon nitride film by cyclic deposition, such as atomic layer deposition, and heat treatment.
2. Description of the Related Art
Integrated circuits fabricated on semiconductor substrates for large scale integration require multiple levels of metal interconnections to electrically interconnect discrete layers of semiconductor devices formed on semiconductor chips. The different levels of interconnections are separated by various insulating or dielectric layers, which are etched to form via holes so as to connect one level of metal to another.
The evolution of chip design continually requires faster circuitry and greater circuit density than before. For faster circuits with greater circuit densities, certain properties are required of materials used to fabricate such integrated circuits, particularly as the dimensions of integrated circuit components are reduced to the sub-micron scale. Also, for greater integrated circuit densities, certain process sequences are required for the manufacture of integrated circuit components.
In recent years, silicon nitride layers deposited at low temperatures (less than 400° C.) have been used in a number of important applications for memory devices, for example, as a passivation layer, a surface protection layer and/or a spacer for a transistor gate. Silicon nitride films may be formed by a plasma enhanced chemical vapor deposition (PECVD) method. The main advantages of the PECVD method over other CVD methods are higher deposition rates, and controllability over a wide range of refractive indices. A further advantage of the PECVD method is that the process can take place at a relatively low temperature, for example temperatures under 400° C., keeping the total thermal budget of the cell processing to a minimum. Furthermore, the PECVD method provides good material properties to films.
However, the PECVD method for forming silicon nitride leads to poor conformality or poor step coverage on a substrate containing small and/or high aspect ratio features. In small circuits and devices, such as ultra-large scale integrated (ULSI) circuitry, poor conformal coverage can hamper the development of higher density circuit devices and elements.
For high conformality of films, cyclic deposition methods such as cyclic CVD, plasma-enhanced atomic layer deposition (PEALD), and thermal ALD are suitable. However, since ALD is a self-limiting adsorption reaction process, the amount of deposited precursor molecules is determined by the number of reactive surface sites and is independent of the precursor exposure after saturation, and a supply of the precursor is such that the reactive surface sites are saturated thereby per cycle. In ALD, reaction occurs on surfaces and forms films thereon, and thus ALD achieves high conformality of films in trenches and holes formed in a substrate. Similarly, since cyclic CVD typically provides gases alternately in cycles to deposit films, it also can improve conformality of films.
However, the present inventors have discovered that although cyclic deposition methods improve conformality of films, the film qualities such as wet etch rate are poor along sidewalls of trenches and holes relative to those of top/bottom surfaces of trenches and holes, especially when the trenches and holes are small (e.g., about 10 nm to about 50 nm in width) and/or have a high aspect ratio (e.g., about 5 to about 20). The present inventors believe that that is because when trenches and holes are small and/or have a high aspect ratio, deposition reactions do not sufficiently progress on sidewalls even if high conformality of films is achieved, and as a result, impurities remain inside the films as residues of reaction gases and/or byproducts of reaction.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.